Organic phosphonic acid compound corrosion protection in aqueous systems

ABSTRACT

The invention disclosed relates to organo-phosphonic acid compounds in combination with zinc salts for use to inhibit metal corrosion in aqueous systems. The organophosphonic acid compounds include alkylene polyphosphonic acids, and the water-soluble salts and esters thereof.

United States Patent 1 Hwa I451 Apr.9, 1974 ORGANIC PIIOSPI-IONIC ACID COMPOUND CORROSION PROTECTION IN AQUEOUS SYSTEMS [75] Inventor: Chih Ming IIwa, Palatine, I11.

[73] Assignee: W. R. Grace & Co., New York,

{22] Filed: Oct. 26. 1972 [21] Appl. No.1 300,938

Related US. Application Data [63] Continuation of Ser. No. 645,600, June 13, 1967, abandoned. Continuation-impart of Ser. No. 581,151, Sept. 22, 1966, Pat. No. 3,431,217.

[56] References Cited UNITED STATES PATENTS 3,483,133 12/1969 Hutch et a1. 252/389 A 3,532,639 10/1970 Hutch et a1. 252/389 A Primary Examiner-Carl D. Quarforth Assistant Eraminer-lrwin Gluck Attorney, Agent, or Firm-Eugene M. Bond 5 7 ABSTRACT The invention disclosed relates to organo-phosphonic acid compounds in combination with zinc salts for use to inhibit metal corrosion in aqueous systems. The organophosphonic acid compounds include alkylene polyphosphonic acids, and the water-soluble salts and esters thereof.

6 Claims, No Drawings ORGANIC PHOSPIIONIC ACID COMPOUND CORROSION PROTECTION IN AQUEOUS SYSTEMS HO \l a in OH ()/OH Formula A P wherein m is an integer from l to R is hydrogen, or an alkyl group having from 1 to 4 carbons and R is hydroxyl, hydrogen, or an alkyl group having from 1 to 4 carbons, R is an alkyl group having 1 to 10 carbons, benzyl or phenyl, R is an aliphatic radical having from 1 to 10 carbons, and the water-soluble salts and esters thereof; or mixtures thereof, and from 1 to 95 weight percent of a water-soluble zinc salt. Aqueous solutions of l to 70 weight percent of this composition are also encompassed within this invention.

In summary, the method of this invention for preventing corrosion of metals in contact with an aqueous liquid comprises maintaining in the aqueous liquid from 1 to 10,000 ppm. of the alkylene polyphosphonic acid, salts or esters thereof, and from 1 to 10,000 ppm. of a water-soluble zinc salt.

Water-soluble inorganic chromates are widely used to treat industrial water systems to prevent corrosion of metal parts in contact therewith. When these chromates are employed alone, they are used in concentrations as low as 200 ppm. and as high as 10,000 ppm., depending upon the protection needed and the permissible cost. When these chromates are used in combinations with molecularly dehydrated inorganic phosphates such as disclosed in U.S. Pat. No. 2,711,391, chromate concentrations as low as ppm. have been found adequate in mild corrosive systems. Therefore, combinations of chromates and molecularly dehydrated phosphates are widely used.

Although chromates are highly effective corrosion inhibitors, their use is subject to several difficulties. Chromates cause serious skin and eye irritations, and chromates cannot be used in aqueous systems such as cooling towers or air-wash units where .the. resulting spray will contact people. Chromate solutions, because they are toxic, often require chemical treatment before being discharged to waste systems. Furthermore, chromates degrade organic compounds mixed therewith, limiting the types or organic compounds which can be mixed with the chromates in dry mixtures and aqueous solutions.

The use of molecularly dehydrated inorganic phosphates in aqueous systems causes serious problems because the polyphosphates hydrolyze to form alkaline earth metal orthophosphates, causing scaling and fouling of the aqueous systems treated. Because of this hydrolysis, excess quantities of the polyphosphates must be employed.

It is an object of this invention to provide a non-toxic composition for treating aqueous systems to prevent corrosion of metal surfaces in contact therewith which does not introduce orthophosphates to the aqueous systems. The composition contains an organic phosphonic acid compound in combination with a water-soluble zinc salt.

The compositions of this invention are useful for treating a variety of aqueous systems, that is, any aqueous system corrosive to metal surfaces in contact therewith. Suitable systems which can be treated according to this invention include water treatment systems, cooling towers, water circulating systems, and the like wherein fresh water, brines, sea water, sewage effluents, industrial waste waters, and the like are circulated in contact with metal surfaces. These compounds are useful in acid pickling baths, radiator coolers, hydraulic liquids, antifreezes, heat transfer mediums, and petroleum well treatments. The process of this invention is suitable for reducing the corrosion of iron, copper, aluminum, zinc and alloys containing these metals such as steel and other ferrous alloys, brass, and the like which are in contact with corrosive aqueous systems.

All concentrationsare given herein as weight percents unless otherwise specified.

The compositions of this invention contain from 1 to percent of an organo-phosphonic acid compound. The preferred organo-phosphonic acid compound for use in the composition of this invention is an alkylene diphosphonic acid having the foregoing Formula A, such as those disclosed in U.S. Pat. Nos. 3,214,454 and 3,297,578, the entire disclosures of which are incorporated herein by reference. Also suitable is an alkylene diphosphonic acid having the foregoing Formula B or Formula C such as those disclosed in U.S. Pat. No. 3,303,139, the entire disclosure of which is incorporated herein by reference. Suitable acids of this type include methylenediphosphonic acid; ethylidenediphosphonic acid; isopropylidenediphosphonic acid; 1- hydroxy, ethylidenediphosphonic acid; hexamethylenediphosphonic acid; trimethylenediphosphonic acid; decamethylenediphosphonic acid; l-hydroxy, propylidenediphosphonic acid; 1,6-dihydroxy, 1,6- dimethyl, hexamethylenediphosphonic acid; 1,4- dihydroxy, 1,4-diethyl, tetramethylenediphosphonic acid; 1,3-dihydroxy, 1,3-dipropyl, trimethylenediphosphonic acid; 1,4-dibutyl, tetramethylenediphosphonic acid, dihydroxy, diethyl, ethylenediphosphonic acid;

4-hydroxy, 6-ethyl, hexamethylenediphosphonic acid: l-hydroxy, butylidenediphosphonic acidl butylidenediphosphonic acid; l-aminoethane-l,l-diphosphonic acid; l-aminopropane-l, l-diphosphonic acid; 1- aminobenzyll l -diphosphonic acid; 1,6- diaminohexanel l ,6,6-tetraphosphonic acid; I- aminoethane-l,l-diphosphonic acid monoethyl ester, and l-amino-Z-phenylethanel ,l-diphosphonic acid. The water-soluble salts of these acids such as the alkali metal, alkaline earth metal, zinc, cobalt, chromium, lead, tin, nickel, ammonium, or amine and lower alkanol amine salts can be used. Also, esters of these acids with an aliphatic alcohol having from 1 to 4 carbons, or mixtures of the above acids, salts or esters can be used. Use of mixtures of any of the general types of organo-phosphonic acid compounds described above is also contemplated within the scope of this invention.

It will be seen from the foregoing listing of acid compounds within the scope of Formula A and a number of the examples which follows, as well as the like compounds disclosed in U.S. Pat. No. 3,214,454 and 3,297,578, that a number of these can be described as methanol phosphonic acid derivatives having the following Formula D:

Formula D R4 OH OH where R is independently selected from the group con sisting of an alkyl group up to four carbon atoms and phosphonate groups, and R is selected from the group consisting of alkyl groups having up to four carbon atoms, when R is a phosphonate group and where n is 0 to 6, when R is an alkyl group; and watersoluble salts thereof.

Specific methanol phosphonic acid compounds thus disclosed include, for example, l-hydroxy ethylidene diphosphonic acid (i.e., ethanol, or methyl methanol, 1,1-diphosphonic acid); l-hydroxy, propylidene diphosphonic acid (i.e., ethyl methanol diphosphonic acid); l,6-dihydroxy-l,6-dimethyl, hexamethylene diphosphonic acid (i.e., tetramethylene bis( methyl methanol phosphonic acid)) and its sodium salt (Examples 44 and 100); 1,4-dihydroxy-l,4-diethyl, tetramethylene diphosphonic acid (i.e., dimethylene bis(ethylmethanol phosphonic acid)); l,3-dihydroxy-I,3-dipropyl trimethylene diphosphonic acid (i.e., methylene bis (propylmethanol phosphonic acid)) and its sodium salt (Examples 46 and 112); dihydroxy, diethyl, ethylene diphosphonic acid (i.e., bis(ethylmethanol phosphonic acid)) and its sodium salt (Examples 52 and 118); and l-hydroxy butylidene diphosphonic acid (i.e., propyl methanol diphosphonic acid).

The compositions of this invention also contain from 1 to 95 and preferably from 25 to 45 percent of a water-soluble zinc salt. It will be seen that the use of the more common water-soluble zinc salts such as zinc nitrate (Zn(NO molecular weight 189) zinc chloride (ZnCl molecular weight 136.29) and zinc sulfate (ZnSO or ZnSO -H O, molecular weight 161.44 and 179.44, respectively) in the aforesaid concentrations will provide zinc ion (Zn" concentrations from as little as 0.345 weight percent (as 1 percent Zn(NO to as high as 45.5 weight percent (equivalent to percent ZnCl Thus the weight ratio of zinc (in the form of one of said water-soluble salts) to phosphonic acid compound may range from about 0.345280 to about 45.521 or, in other words, from about 1:232 to about 110.022. At the preferred concentrations of zinc salt the weight ratio of zinc ion may range from about 8.64:80 (Zn equivalent in 25 weight percent of Zn(NO to about 21.5:1 (Zn equivalent in 45 weight percent of ZnClor in other words, from about 11927 to about 120.0465. As seen in the following specific Example 4, a typical zinc to phosphonic acid compound weight ratio is 1:1.

The zinc salts which can be employed in the composition of this invention include any water-soluble zinc salt such as zinc sulfate, zinc chloride, zinc nitrate, alkali metal-zinc phosphate glasses, crystalline alkali metalzinc polyphosphates, and the like.

Aqueous systems can be treated with aqueous solutions containing from 1 to 70 percent and preferably from 1 to 10 percent of the compositions of this invention. These solutions can be made by premixing the ingredients of this composition and then adding the mixture to water, or by adding the individual ingredients of the composition of this invention separately to water. These aqueous feed solutions are stable and can be stored prior to use.

In the methods of this invention for preventing corrosion of metals in contact with aqueous liquids, from 1 to 10,000 ppm. and preferably from 1 to of the organophosphonic acid compounds, and from 1 to 10,000 ppm. and preferably from 2 to 200 ppm. of the water-soluble zinc salts are maintained in aqueous liquid.

The aqueous corrosion resistant solutions of this invention are solutions of at least 1 and preferably from 5 to 200 ppm. of the compositions of this invention. The ingredients can be added to the aqueous solution either in premixed solid or solution or individual solids or solutions to form this aqueous solution composition.

The compositions of this invention are non-toxic and prevent corrosion of metals in contact with aqueous liquids. These compositions can be substituted for chromate base corrosion inhibitors previously used where the toxicity of the chromate makes its use undesirable or where disposal of corrosion inhibiting solutions containing chromates raises serious water pollution problems requiring extensive pretreatment to remove the chromates prior to disposal of such solutions. The compositions of this invention in aqueous solutions prevent corrosion of metal parts such as heat exchangers, engine jackets, and pipes and particularly prevent metal loss, pitting, and tuberculation of iron base alloys, copper alloys, and aluminum alloys in contact with water.

This invention is further illustrated by the following specific but non-limiting examples.

EXAMPLE 1 This example demonstrates the synergistic reduction in corrosion rates obtained with the compositions of this invention.

In this test, circulating water having the following composition was used:

Calcium sulfate dihydrate 445 ppm. Magnesium sulfate heptahydrate 519 ppm. Sodium bicarbonate 185 ppm. Calcium chloride l36 ppm.

During the test, the circulating water was fed to a closed circulating test system at a rate of 5 gallons per day, the ove rflow from the test system being discharged to waste.

In the closed circulating system, circulating water having a temperature of 130 F. and pH of 6.5-7.0 was fed at a rate of one gallon per minute to a coupon chamber containing test coupons for the corrosion test. Water from the coupon chamber was then passed through an arsenical admirality brass tube surrounded by a jacket through which a heating fluid having an initial temperature of 240 F. was countercurrently passed. The circulating water was then cooled to 130 F. and recirculated through the system. The total circulating time for each test was days.

Mild steel coupons having an average area of 26.2 cm. were used in the test chamber. The coupons were carefully cleaned and weighed before use. Following the test, each coupon was cleaned with inhibited hydrochloric acid, rinsed, dried and weighed to determine the corrosion rate in mils per year. A comparison of the corrosion rates of the individual ingredients of the composition of this invention with combination of these ingredients according to this invention were found to be as shown in Table A.

As shown in Table A, Example 4 corresponding to the composition of this invention provides a corrosion protection far greater than would be expected in view of the effects of the individual components thereof.

Examples of other compositions accordong to this invention are shown in Table B.

TABLE B Example No. Ingredients wt.

5 Zinc chloride 40.0%; hydroxy ethylidene diphosphonic acid 60.0%

6 Magnesium methylenediphosphonate 30%;

zinc sulfate monohydrate 70% 7 Zinc isopropylidenediphosphonate 30%;

zinc sulfate monohydrate 70% 8 Sodium trimethylenediphosphonate 30%;

zinc sulfate monohydrate 70% 9 Decamethylenediphosphonic acid 30%;

zinc sulfate monohydrate 70% 10 Sodium 1,6-dihydroxy, 1.6-dimethyl,

hexamethylene-diphosphonate 30%; zinc sulfate monohydrate 70% 1-amino-2-phenylethane-l,l-diphosphunic acid 30%; zinc sulfate monohydrate Sodium l,3 dihydroxy, l,3-dipropyl,

trimethylene-diphosphonate 30%; zinc sulfate monohydrate 70% Zinc l-aminoethane-l ,l-diphosphonate 30%; zinc sulfate monohydrate 70% 14 l'aminoethane-l,l-diphosphonic acid monoethyl ester 30%; zinc sulfate monohydrate 70% 30%; zinc sulfate monohydrate What is claimed is:

l. A composition useful for inhibiting corrosion in aqueous systems, said composition consisting essentially of one part by weight zinc in the form of a watersoluble zinc salt and from 0.02 to about 300 parts by weight of a water-soluble organic phosphonate compound having the formula where R is independently selected from the group consisting of alkyl groups up to four carbon atoms, and phosphonate groups, and R is selected from the group consisting of alkyl groups having up to four carbon atoms, when R is a phosphonate group; and

where n is 0 to 6, when R is an alkyl group; and watersoluble salts and esters thereof.

2. The composition of claim 1 in which the watersoluble zinc salt is zinc sulfate.

3. The composition of claim 1 in which the phosphonate compound is ethanol 1,1-diphosphonicacid or water-soluble salt thereof.

4. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous systems at least about one part per million of the composition of claim 1.

5. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about one part per million of the composition of claim 2.

6. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about one part per million of the composition of claim 3. 

2. The composition of claim 1 in which the water-soluble zinc salt is zinc sulfate.
 3. The composition of claim 1 in which the phosphonate compound is ethanol 1,1-diphosphonic acid or water-soluble salt thereof.
 4. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous systems at least about one part per million of the composition of claim
 1. 5. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about one part per million of the composition of claim
 2. 6. A method of inhibiting corrosion in aqueous systems comprising adding to said aqueous system at least about one part per million of the composition of claim
 3. 